Three microliters of the T. thermophilus sample, diluted to 0.02 mg/mL, was placed onto the surface of the carbon-coated grid. The sample was blotted off and replaced with 3 microliters of 2% uranyl acetate. The uranyl acetate was blotted away and replaced with 3 microliters of 4% methylamine tungstate. The final drop of methylamine tungstate was blotted away and the grid was left to air dry.

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Atomic model buiding

Modeling #1

Software: EMfit / Refinement protocol: rigid body / Target criteria: sumf and number of atoms inside density / Refinement space: REALDetails: Protocol: Each chain was fit as a separate rigid body. X-ray coordinates for the bovine alpha3 beta3 and gamma sub-assemblies were manually fitted into the EM density using the program O. The program EMfit (Rossmann et al., 2001) was then used in order to obtain a more quantitative fit.Input PDB model: 1E79Chain ID: 1E79_A, 1E79_B, 1E79_C, 1E79_D, 1E79_E, 1E79_F, 1E79_G

Modeling #2

Software: EMfit / Refinement protocol: rigid body / Target criteria: sumf and number of atoms inside density / Refinement space: REALDetails: Protocol: Each chain was fit as a separate rigid body. X-ray coordinates for the bovine alpha3 beta3 and gamma sub-assemblies were manually fitted into the EM density using the program O. The program EMfit (Rossmann et al., 2001) was then used in order to obtain a more quantitative fit.Input PDB model: 1R5Z

Software: EMfit / Refinement protocol: rigid body / Target criteria: sumf and number of atoms inside density / Refinement space: REALDetails: Protocol: Each chain was fit as a separate rigid body. X-ray coordinates for the bovine alpha3 beta3 and gamma sub-assemblies were manually fitted into the EM density using the program O. The program EMfit (Rossmann et al., 2001) was then used in order to obtain a more quantitative fit.Input PDB model: 1C17